Refrigeration systems are commonly used in supermarkets to refrigerate or to maintain in frozen state perishable products, such as foodstuff.
Conventionally, refrigeration systems include a network of refrigeration compressors and evaporators. Refrigeration compressors mechanically compress refrigerant vapor, which is circulated from the evaporators, to increase its temperature and pressure. The resulting high-temperature refrigerant vapor, under high-pressure, is circulated to a refrigerant condenser where the latent heat from the vapor is absorbed. As a result, the refrigerant vapor liquefies into refrigerant liquid. The refrigerant liquid is circulated through refrigerant expansion valves, thereby reducing the temperature and pressure, to the evaporators wherein the refrigerant liquid evaporates by absorbing heat from the surrounding foodstuff.
Refrigeration systems as described above which use a single refrigerant typically require a significant amount of such refrigerant. Thus, should leaks occur in such a system, there is a risk of substantial amounts of refrigerant being leaked into the environment or into foodstuffs. Since leaked refrigerant may be damaging to the environment and to foodstuffs, such a situation is highly undesirable.
Use of dual refrigerant systems, i.e. having a primary and a secondary refrigerant, may, to a certain extent attenuate this problem, as only a secondary refrigerant, cooled by a primary refrigerant, is circulated in secondary evaporators near the foodstuffs. Thus, even if a leak develops in these secondary evaporators, only secondary refrigerant will be affected. However, since it is secondary refrigerant which actually cools the foodstuffs, this is only a partial solution since leaks of secondary refrigerant will eventually lead to deterioration of refrigeration capacity of the system, as well as possibly to damage of the foodstuffs. Further, such dual refrigerant systems often require circulation, i.e. flow, of large amounts of secondary refrigerant through the evaporators for cooling foodstuffs at any given moment. Obviously, use of large amounts of secondary refrigerant continues to leave the system vulnerable to leaks and is also costly due to the amount of secondary refrigerant that must be supplied.
Accordingly, it would be useful to have a dual refrigerant system in which flow of secondary refrigerant flow is reduced for increasing efficiency and decreasing vulnerability to leaks.